In many applications, a human operator must manipulate a heavy load which would ordinarily be beyond his or her physical abilities. One example is a factory assembly worker placing an automobile engine into an engine compartment. Another example is a test engineer aligning a electronic test head associated with a test station to a target system for embedded testing. Several prior art systems use counterbalancing techniques to allow an operator to manipulate such loads with little effort relative to the weight of the load. Prior art systems counterbalance with counterweights, constant force springs, air cylinder actuators with pressure regulators, conventional compression/extension springs, gas springs and combinations thereof. Counterweights, constant force springs and air cylinder actuators can counterbalance a constant load along a considerable length of travel, but they cannot counterbalance a load which varies with position or other physical parameters. As a result, the effort necessary to move a load varies as the load varies. Conventional springs and gas springs can counterbalance a variable load if the load variation coincides with the spring constant, but they cannot counterbalance over any considerable range of travel. The range of travel of conventional and gas springs is limited by the range of the spring itself. Use beyond the spring range will result in non-linear characteristics and eventually mechanical failure.
There is a need for a counterbalancing system which can counterbalance a load which varies with respect to position and other physical parameters over a significant, useful range of travel.
Accordingly, it is an object of this invention to provide an improved counterbalancing system for counterbalancing a variable load over a considerable range of travel.
Other objects and advantages of the present invention will become apparent upon consideration of the appended drawings and description thereof.